1. Field of the Invention
This invention relates to a method and apparatus for treating surfaces of objects such as semiconductor wafers (hereinafter called "wafers" for simplicity) and other small objects with chemical treatment liquid.
2. Description of the Prior Art
As well known in production processes of semiconductor devices, various surface treatments such as etching, removing of photoresist films, wafer cleaning, etc, are repeated. An apparatus available for achieving a series of such surface processings automatically is disclosed, for instance, in Japanese Patent Laying Open Gazette No. 52-150974 (1977), wherein various treatment baths and a drier are arranged in a line and a transfer machine or conveying machine moving along the line is provided. Cassettes each holding a lot consisting of a plurality of wafers are held by a handling mechanism of the transfer machine and dipped successively in treatment liquids filled in the treatment baths. Such treatment sequence is carried out automatically in response to command signals supplied from a controller comprising a microcomputer and others.
However, in the conventional treatment apparatus, the transport of cassettes should be interrupted momentarily during replacement or addition of the treatment liquids, which is required because of a deterioration of the treatment liquid due to the repeated dippings and the lapse of time. For example, consider an apparatus, illustrated schematically in FIG. 1 as a conceptional overview thereof, in which a loader L, treatment baths P.sub.1, W.sub.1 . . . W.sub.4, a drier D and an unloader UL are aligned along a transporting path of a transporting machine T so that the treatments are carried out in the order of the alignment. When the treatment liquid of the treatment bath P.sub.2 is being replaced, the following cassette to be dipped in the bath P.sub.2 should be kept waiting in the treatment bath W.sub.1 positioned just before the bath P.sub.2.
Therefore, the flow of the cassettes becomes intermittent, reducing the processing efficiency as a whole. Furthermore, during such replacement of the treatment liquid in one of the treatment baths, the deterioration of treatment liquids continues to take place in all other baths, resulting in a significant problem of inhomogeneous surface treatments of wafers lot by lot. Further, the number of replacements of the treatment liquids required for treatment of a certain number of lots is increased due to the deterioration, resulting in a low economical efficiency.
Especially, the integration density of integration circuits build up on surfaces of semiconductor wafers has increased recently, therefore, a provision of a dustfree atmosphere during formation of fine patterns and a uniform liquid quality control is important and is a big problem to be solved. To this end, liquids suffering rapid deterioration with time, for example, a cleaning liquid consisting of H.sub.2 SO.sub.4 and H.sub.2 O.sub.2, requires frequent replacement thereof and sometimes the replacement is necessary for every dipping of the wafers. Once the treatment liquid is drained once out of the bath, it takes a long time interval for cleaning of the inside of the bath, a supply of new liquid and the temperature increase thereof, while the bath cannot be used during such activity.